1. Field
The presently disclosed subject matter relates to surface mount devices, and more particularly to reliable surface mount devices including a ceramic package and a semiconductor optical chip such as an LED, a laser diode, a photo diode, etc.
2. Description of the Related Art
Surface mount devices are used for semiconductor light-emitting devices such as an LED and the like and for semiconductor light-receiving devices such as a photo transistor, etc. Surface mount LED devices are used for LCD back light units in mobile phones, digital video cameras, PDAs, etc., since white LEDs have been available on the market. Surface mount LED devices have been recently employed as a light source for vehicle lamps and for general lighting and the general application of LEDs and other surface mount lighting devices have been expanded.
Surface mount devices have also been miniaturized. However, because it is desired for semiconductor light-emitting/light-receiving devices to emit/receive greater amounts of light flux (and in view of the above-described applications being expanded from small size usage such as in indicators, to larger size usages such as in general lighting and vehicle lamp lighting), demand has increased for surface mount devices that can be used for a high flux type apparatus and/or a wide-screen apparatus.
However, because high flux type LEDs are generally driven by a large current, their rated wattages and heating values become large, and also the high flux type LEDs are frequently used under a harsh environment such as high temperature and high humidity and the like, especially when they are used for vehicle lamps, outdoor lighting, etc. A ceramic package has been used for the surface mount devices because the ceramic package has a high radiating performance and a good heat resistance property as compared with either a resin molding package or a plastic package.
A conventional semiconductor device and method for manufacturing the same using a ceramic package is disclosed in patent document No. 1 (Japanese Patent Application Laid Open JP2005-159311). FIGS. 1a and 1b are front and side views, respectively, depicting a conventional side view type semiconductor device using a ceramic package that is disclosed in patent document No. 1.
The conventional side view type LED light source 1 includes: a ceramic package 2; an LED chip 4 mounted in the ceramic package 2 so as to emit light parallel to a mounting surface of a mounting board 5; and electrode pads 3a and 3b located so as to face the mounting surface. When the LED light source 1 is mounted on the mounting surface, the LED light source 1 can be mounted on the mounting board 5 by fixing each of the electrode pads 3a, 3b thereof to conductor patterns 6a, 7b formed on the mounting board 5 via solders 7a, 7b, respectively.
A method for manufacturing the ceramic package 2 includes: providing an inner plate that is dried after printing a metallic paste such as Au, Ag, Cu and the like on an unsintered ceramic plate; providing a tubular body that includes an opening for a cavity on another unsintered ceramic plate; overlapping the tubular body on the inner plate via a glass paste; and sintering the tubular body and the inner plate at a desirable temperature. The LED light source 1 can be made by encapsulating the LED chip 4 in the cavity with an encapsulating resin after the LED chip 4 is mounted on a bonding pad that is formed by drying the metallic paste.
An alumina, an aluminum nitride that has thermal conductivities nearly equal to that of aluminum, and the like, are used as the ceramic material, a. A glass epoxy board is frequently used as the mounting board 5. A metallic circuit board is also used as the mounting board 5 when the LED light source 1 is used to radiate heat generated from the LED chip such as a high flux type LED light source and so on. The metallic circuit board is made by forming conductive patterns on an insulating layer after the insulating layer is formed on a metallic palter having a high thermal conductivity such one that includes aluminum, etc.
In a soldering process for LED light sources, after a soldering paste is printed on a mounting board, the LED light source is mounted on a connecting location of the mounting board and is connected thereto mainly by a reflow soldering process in which the solder paste is melted using a heat source. The one reason for using this type of process is that electronic parts are miniaturized and also are closely mounted, and the other reason is that a solder including mercury is replaced with a mercury-free solder.
The above-referenced Patent Document is listed below, and is hereby incorporated with its English abstract in its entirety.    1. Patent Document No. 1: Japanese Patent Application Laid Open JP2005-159311
As described above, the ceramic package has characteristics such as permitting high radiating performance and excellent heat resistance properties in comparison with a resin molding package and/or plastic package, and therefore the ceramic package has been recently studied by the scientific community. An alumina, an aluminum nitride of which thermal conductivity is nearly equal to that of aluminum, and the like are used as the ceramic material. However, when heat generated from the ceramic package should be radiated to the outside, it may not be adequate to radiate the heat using the ceramic package alone.
Therefore, the ceramic package is attached to a metallic plate via a thermal conductive adhesive, or it can be mounted on the metallic circuit board based upon aluminum for practical purposes. However, when the LED light source using the ceramic package is mounted on the metallic circuit board based on aluminum having a high thermal conductivity, because the temperature of the LED light source is increased due to an ambient temperature and heat generated from other parts mounted on the circuit board, conditions for use of the LED light source become harsher.
Thus, because a difference between the temperature of the ceramic package during operating the LED light source and the non-operating temperature becomes very large, a difference between coefficients of thermal expansion of the mounting circuit board and the ceramic package causes the ceramic package to experience thermal fatigue. The thermal fatigue may cause cracks in connection(s) between the mounting circuit board and the ceramic package, and consequently may cause a disconnection between the LED light source and the mounting circuit board.
The disclosed subject matter has been devised to consider the above and other problems and characteristics. Thus, embodiments of the disclosed subject matter can include surface mount devices with high reliability even under a harsh environment and which can be made with a simple manufacturing process, and can include surface mount LED devices that can prevent cracks from forming in the ceramic package in the connection between the mounting board and the ceramic package under the above-described harsh environment.